Briefly describe the main differences between fast and slow twitch muscles and how does this relate to their specific functions.

First of all,  slow-twitch (type I) muscle fibres have a large number of mitochondria allowing them to carry out aerobic respiration at a high rate by providing a site for the Kreb's cycle (taking place in the mitochondrial matrix) and for the Electron Transport Chain (at the inner membrane of a mitochondrium).  Moreover, the slow-twitch muscle cells appear much darker under the microscope due to a significantly larger amount of myoglobin, which is a protein similar to haemoglobin, binding oxygen and storing it inside the cells; type I muscles also have a much better blood supply because of a high number of capillaries in their vicinity - therefore more oxygen can be provided. Those features of the type I muscle fibres allow them to sustain work for a long period without producing much lactic acid and causing fatigue as they rely on oxidative phosphorylation as the main source of ATP. This makes slow-twitch muscles very useful for a The fast-twitch (type II) muscle fibres on the other hand have very few mitochondria and not very much myoglobin and poorer blood supply than type I muscle fibres, leading to their lighter colouration. This makes type II muscle more reliant on glycolysis and creatine phosphate as their main source of ATP and so they fatigue faster an their slower counterparts. However, due to their capability to produce comparable tension 2-3 times faster than type I muscles, they are capable of quick but short bursts of muscle activity. This makes them very useful for short but intense activities such as sprinting.